1. Field of the Invention
The present invention relates generally to a liquid crystal display device, and more particularly to a liquid crystal display device having a transmissive display function of displaying an image by selectively passing backlight.
2. Description of the Related Art
A liquid crystal display device having a transmissive display function includes a transmissive liquid crystal display panel and a backlight unit which illuminates the liquid crystal display panel from the back side thereof. The liquid crystal display panel is configured such that a liquid crystal layer is held between a pair of substrates. The liquid crystal display panel has an active area for displaying an image and a light-shield area which surrounds the active area.
In a color-display-type liquid crystal display device, each of pixels which constitute the active area includes a pixel electrode and a color filter. The color filters of the respective pixels are disposed spaced apart from one another, for example, in order to prevent occurrence of non-uniformity in gap of the liquid crystal layer due to irregularities which are formed by overlapping of the color filters. Thus, a light-shield layer (black matrix) is disposed between the pixels in the active area, as in the light-shield area. In the light-shield area, color filters are disposed, as in the active area, for example, in order to secure the same gap as in the active area. A counter-electrode is so disposed as to cover the color filters, and the counter-electrode extends not only over the active area but also over the outside of the active area (i.e. over the light-shield area) in consideration of misalignment in attachment between the substrates.
In the liquid crystal display device having the above-described structure, when a voltage is applied to the liquid crystal layer, a vertical electric field is generated substantially in a normal direction to the liquid crystal display panel between the pixel electrode of each pixel and the counter-electrode. At this time, the pixels that are disposed at end portions of the active area suffer the influence of an oblique electric field, which is generated aside from the vertical electric field. Specifically, an oblique electric field, which is inclined with respect to the normal line of the liquid crystal display panel, is generated between the counter-electrode, which covers the active-area-side end faces of the color filters disposed on the light-shield area, and the pixel electrodes disposed at end portions of the active area.
There is a concern that a defect in alignment of liquid crystal molecules in the liquid crystal layer may occur in the pixels at the end portions of the active area due to interactions between the oblique electric field and the vertical electric field. In the transmissive liquid crystal display panel, such a defect in alignment causes so-called “light leakage”, by which backlight passes through the liquid crystal layer regardless of the voltage that is applied to the liquid crystal layer.
Jpn. Pat. Appln. KOKAI Publication No. 2002-357828 (Patent Document), for instance, discloses a technique in which a surface stepped-portion in each pixel is set at less than 1.9 μm, or the angle between an oblique part of the surface stepped-portion in each pixel and the surface of the display area is set at 10° or less, thereby to improve the defect in alignment of liquid crystal molecules (or abnormality in alignment).
According to the above-described Patent Document, consideration is given to the surface stepped-portion that is formed when the color filters of neighboring pixels are overlapped in the liquid crystal display device of the color filter on array (COA) configuration. Thus, it is still difficult to prevent light leakage due to a defect in alignment in pixels at end portions of the active area.